Suggest two ways in which the student’s diagram fails to show the positions and motion of the molecules accurately.
Some of the molecules of a liquid evaporate. Describe what happens during evaporation.
Explain why evaporation has a cooling effect on the liquid.
The beaker shown in Fig. 10.2 contains pure water at a temperature of $80^\circ\text{C}$. A thermometer, initially at room temperature, is placed in the air just above the water. The reading on the thermometer starts to increase slowly. Explain how convection in the air causes the reading on the thermometer to increase.
A heater is placed below the beaker and the water boils violently, producing steam. The thermometer reading rises rapidly. Explain how the water in the gas state transfers thermal energy (heat) to the thermometer.
The heater below the beaker has a power of $200\,\text{W}$. The beaker initially contains $100\,\text{g}$ of water. The water is heated for $120\,\text{s}$. Calculate the thermal energy produced by the heater in $120\,\text{s}$.
Calculate the thermal energy needed to heat the water from $80^\circ\text{C}$ to $100^\circ\text{C}$.
Calculate the thermal energy needed to reduce the mass of water in the beaker.
Calculate the thermal energy produced by the heater that does not pass to the water.